Vibration detector

ABSTRACT

A small photodetector type microphone ( 10 ) exhibiting excellent directivity without requiring any mirror surface. A diaphragm ( 27 ) vibrates in response to a sound pressure. An optical waveguide ( 28 ) is formed along the diameter of the diaphragm ( 27 ) and integral vibration of the optical waveguide ( 28 ) and the diaphragm ( 27 ) causes a variation in the quantity of light leaking from the optical waveguide ( 28 ) to the outside thus causing a variation in the quantity of light being transmitted across the optical waveguide ( 28 ). The optical waveguide ( 28 ) has one end side for introducing light into a light emitting elements ( 20 ) and the other end side for delivering light to a light receiving element ( 24 ). The light receiving element ( 24 ) outputs an electric signal related to the quantity of incident light.

TECHNICAL FIELD

[0001] The present invention relates to a vibration detector applicableto a microphone for example, and more particularly to a vibrationdetector for detecting vibration by utilizing light.

BACKGROUND ART

[0002] A general microphone converts a displacement of the diaphragmvibrating in response to a sound pressure into an electric signal byusing a coil or capacitor. A microphone has been proposed which is ofthe type that vibration of the diaphragm is converted into an electricsignal by utilizing light. A known microphone of such a light use typewill be described with reference to FIGS. 15 to 17. In a light detectiontype microphone 70 shown in FIG. 15, a diaphragm 72 mounted on the frontside of a case 71 has a mirror surface on the inner side and vibratesback and forward in response to a propagating sound wave. The case 71having a mirror surface of the inner wall has the diaphragm 72 mountedon the front opening end and receiving a sound pressure and a partitionplate 75 for leaving a gap 76 between the top of the partition plate 75and the diaphragm 72 and partitioning the inside of the case 71excepting the gap 76 into two rooms. A light emitting element 73 and alight receiving element 74 are disposed in the partitioned roomsopposite relative to the partition plate 75. Light emitted from thelight emitting element 73 is reflected at the inner mirror surface ofthe diaphragm 72, passes through a gap 76 and enters the light receivingelement 74. A condenser lens 78 is disposed on an optical path betweenthe light emitting element 73 and diaphragm 72 and converges light at apredetermined position of the diaphragm 72. A condenser lens 79 isdisposed on an optical path between the diaphragm 72 and light receivingelement 74 and converges light reflected by the diaphragm 72 at thelight receiving element 74. The size of the gap 76 changes with avibration displacement of the diaphragm 72 so that a light receptionquantity of the light receiving element 74 is a function of a vibrationdisplacement quantity of the diaphragm 72. An electric signal related toa sound pressure can thus be generated from a light reception quantityof the light receiving element 74.

[0003]FIGS. 16 and 17 are a schematic diagram and a detailed diagramshowing a light detection type microphone 83 utilizing light accordingto another conventional technique. A monitor photodiode 85 detects aquantity of laser light irradiated from a semiconductor laser 84. Alaser APC 86 controls an output of the semiconductor laser 84 inaccordance with an output of the monitor photodiode 85, to thus maintainconstant a radiation quantity of the semiconductor laser 84 duringoperation. A diaphragm 89 disposed in front of the semiconductor laser84 has a mirror surface on the inner side and vibrates in response to asound pressure. A laser beam from the semiconductor laser 84 passesthrough an objective lens 90 and becomes incident upon the diaphragm 89.The reflected light passes through the objective lens 90 and becomesincident upon a diaphragm displacement detector diode 91 which detects alight quantity. Referring to FIG. 17, each element shown in FIG. 16excepting the diaphragm 89 is housed in a case 93. The peripheral of thediaphragm 89 is supported by the front wall of the case 93. The case 93has a plurality of communication holes 94 for making the inner surfaceside of the diaphragm 89 communicate with an external. The semiconductorlaser 84 and diaphragm displacement detector diode 91 are mounted on amount substrate 96. A laser beam from the semiconductor laser 84 isirradiated to the inner mirror surface of the diaphragm 89 via areflected light flux splitting element 97, the objective lens 90 and anachromatic transparent lid 98. The reflected light becomes incident uponthe diaphragm displacement detector diode 91 via the achromatictransparent lid 98, objective lens 90 and reflected light flux splittingelement 97. The achromatic transparent lid 98 prevents a sound pressurefrom propagating via an opening over which the lid is mounted. Afocussing actuator 99 controls the position of the objective lens 90along the axial direction by utilizing known focus servo control to beused by a compact disc (CD) player or the like. More specifically, theposition of the objective lens 90 along the axial direction iscontrolled in accordance with the frequency components, for example,lower than 20 Hz (low frequency components lower than audible frequency)of a focus error signal detected with the diaphragm displacementdetector diode 91. Regardless of vibration of the diaphragm 89, thefocus of the laser beam can be positioned on the diaphragm 89. A soundpressure in the audible frequency range can be detected by deriving thefocus error signal at 20 Hz or higher from the diaphragm displacementdetector diode 91.

[0004] The light detection type microphone 70 shown in FIG. 15 isassociated with the following problems. It is difficult to adjust thegap 76 in a sound pressure light reception region where a linearrelation between a sound pressure and a light reception quantity can beobtained. A light reception quantity of the light receiving element 74is likely to vary because of a variation in a divergence angle of lightemission of the light emitting element 73 and a variation in a directionof the light emitting element 73. The light detection type microphone 83shown in FIGS. 16 and 17 is associated with the following problems.Although a variation in the characteristics of each element and avariation in the mount position of each element can be suppressed, thelayout of components becomes long along the axial direction and acompact layout is difficult. In order to improve the directivity of themicrophone, it is necessary to react a sound pressure from a soundsource also with the inner surface of the diaphragm 89. However, if thediaphragm 89 is positioned near at the objective lens 90 in order tomake compact the light detection type microphone 83, the objective lens90 hinders the propagation of a sound pressure to the inner surface ofthe diaphragm 89, resulting in a degraded directivity. It is necessaryfor the light detection type microphone 83 to apply a spot of a laserbeam to the diaphragm 89 and detect the reflected light. It is thereforenecessary to maintain always clean the inner mirror surface of thediaphragm 89. However, the inner mirror surface of the diaphragm 89 islikely to be blurred because of chemical reaction of chemical gascontained in the atmospheric air at a small quantity and because ofattachment of dust.

DISCLOSURE OF THE INVENTION

[0005] An object of the invention is to provide a vibration detectorcapable of preventing the linearity of vibration amplitude—electricsignal from being degraded by an assembly variation.

[0006] Another object of the invention is to provide a vibrationdetector capable of being made compact while maintaining a gooddirectivity.

[0007] A vibration detector according to a first embodiment comprises: adiaphragm which vibrates upon reception of vibration; and an opticalwaveguide which extends along a direction of a flat plane of thediaphragm and equipped with the diaphragm to vibrate integrally with thediaphragm, wherein: in accordance with deformation of the opticalwaveguide caused by vibration of the diaphragm, a leak light quantity oflight entered from one end of the optical waveguide and leaked to anoutside of the optical waveguide changes and a light propagationquantity of the light propagated to the other end of the opticalwaveguide changes; and a displacement of the diaphragm caused by thevibration is detected by detecting a change in the light propagationquantity of the optical waveguide.

[0008] This vibration detector can be used not only as a microphone fordetecting sound pressure vibration propagating in gas but also as adetector for detecting liquid pressure vibration and solid vibrationpropagating in liquid and solid.

[0009] In the first invention, the optical waveguide may be formedintegrally with the diaphragm or adhered to the diaphragm. The vibrationdetector is preferably equipped with a light emitting element forirradiating light to the optical waveguide and a light receiving elementfor detecting a quantity of light output from the optical waveguide. Thelight emitting element, light receiving element and an element forprocessing a light reception quantity of the light reception element maybe mounted outside of the vibration detector. In this vibrationdetector, it is not necessary to use a long layout of optical elementsalong the vibration direction of the diaphragm or along the optical axisdirection of a lens. The vibration detector can therefore be madecompact. Since a mirror surface is unnecessary, problems ofcontamination of the mirror surface can be eliminated. If the vibrationdetector is applied to a microphone, a good directivity can be obtainedbecause an optical element such as an objective lens is not mounted nearat the back surface of the diaphragm in order to make the microphonecompact.

[0010] According to a vibration detector of a second invention, in thevibration detector of the first invention, in accordance with thedeformation of the optical waveguide caused by vibration of thediaphragm, a material density of a deformed portion of the opticalwaveguide changes to thereby change a refractive index of the deformedportion; and he leak light quantity of light from the optical waveguidechanges with a change in the refractive index.

[0011] In a vibration detector of a third invention, a diameter orthickness of the optical waveguide along a vibration direction of thediaphragm is set so that the leak light quantity of light from theoptical waveguide changes more or less in accordance with thedeformation of the optical waveguide.

[0012] The shape of a cross section of the optical waveguide may berectangle, square, circle, ellipse or the like.

[0013] According to a vibration detector of a fourth indention, in thevibration detector of the first invention, a refractive index of theoptical waveguide is set irregularly so that the leak light quantity oflight from the optical waveguide changes with the deformation of theoptical waveguide.

[0014] According to a vibration detector of a fifth indention, in thevibration detector of the first invention, the optical waveguide has adiscontinuous region at a proper position along an extension directionof the optical waveguide; end positions of the optical waveguideconfronting with each other with the discontinuous region beinginterposed therebetween relatively displace toward a vibration directionin response to the vibration of the diaphragm; and in accordance withthe relative displacement, the leak light quantity of light from thediscontinuous region of the optical waveguide changes.

[0015] According to a vibration detector of a sixth indention, in thevibration. detector of the first invention, the optical waveguide isequipped in the diaphragm.

[0016] A vibration detector according to a seventh invention comprises:a diaphragm having a deflection region which deflects along a vibrationdirection upon reception of vibration; an optical waveguide having adeflection optical waveguide region which deflects integrally with adeflection region of the diaphragm wherein a light propagation quantitychanges with deflection of the deflection optical waveguide region; alight emitting element for making light become incident upon one end ofthe optical waveguide; and a light receiving element for receiving lightoutput from the other end of the optical waveguide and outputting achange in the light propagation quantity of the optical waveguide as anelectric signal representative of a displacement quantity of thedeflection region of the diaphragm.

[0017] According to the seventh invention, the diaphragm includes adiaphragm having a plate-like vibration member. The vibration member maybe a member which vibrates upon reception of vibration propagated viaair, liquid or solid, or may be a vibration source itself. In order tomake the vibration member vibrate upon reception of vibration propagatedvia solid, the housing of the vibration detector may be fixed to thesolid on the side of the vibration source so that the vibration membervibrates relative to the housing, or alternatively a predeterminedvibration propagating rod may be abut upon the vibration member. Thevibration detector includes at least a microphone. In the seventhinvention, the element for processing an electric signal from the lightreceiving element may be equipped with the vibration detector or may bemounted outside of the vibration detector.

[0018] According to a vibration detector of an eighth invention, in thevibration detector of the seventh invention, the optical waveguidetogether with the diaphragm is held by an optical waveguide holder andoptically coupled to the light emitting element and the light receivingelement via the optical waveguide holder.

[0019] According to a vibration detector of a ninth invention, in thevibration detector of the seventh invention, the deflection opticalwaveguide region of the optical waveguide is formed continuously in anarea corresponding to the deflection region of the diaphragm; inaccordance with deformation of the deflection optical waveguide regioncaused by vibration of the diaphragm, a material density of thereflection optical waveguide region changes to thereby change arefractive index of the deflection optical waveguide region; and a leaklight quantity of light from the deflection optical waveguide regionchanges with a change in the refractive index.

[0020] According to a vibration detector of a tenth invention, in thevibration detector of the seventh invention, the deflection opticalwaveguide region of the optical waveguide is formed continuously in anarea corresponding to the deflection region of the diaphragm; and adiameter or thickness of the deflection optical waveguide region along avibration direction of the diaphragm is set so that a leak lightquantity of light from the deflection optical waveguide changes more orless in accordance with deformation of the deflection optical waveguideregion caused by vibration of the diaphragm.

[0021] According to a vibration detector of an eleventh invention, inthe vibration detector of the seventh invention, the deflection opticalwaveguide region of the optical waveguide is formed continuously in anarea corresponding to the deflection region of the diaphragm; and arefractive index of the deflection optical waveguide region is setirregularly so that a leak light quantity of light from the deflectionoptical waveguide region changes with deformation of the deflectionoptical waveguide region.

[0022] In forming the optical waveguide, for example, thermal diffusionor ion implantation adopted by semiconductor manufacture techniques maybe used. Predetermined optically transmissive material (e.g., lithiumnitrate LiNO₃) is selectively subjected to an ion exchange process. Withthis ion exchange process, a refractive index of the portionion-exchanged is changed from that of the portion not ion-exchanged sothat the optical waveguide whose refractive index is not uniform can beformed. In forming the optical waveguide, for example, a plurality ofmetal thin films or dielectric films having different refractive indicesmay be pressure bonded or laminated.

[0023] According to a vibration detector of a twelfth invention, in thevibration detector of the seventh invention, the deflection opticalwaveguide region of the optical waveguide has a discontinuous region ata position corresponding to the deflection region of the diaphragm; endpositions of the deflection optical waveguide region confronting witheach other with the discontinuous region being interposed therebetweenrelatively displace toward a vibration direction in response to thevibration of the diaphragm; and in accordance with the relativedisplacement, a leak light quantity of light from the discontinuousregion changes.

[0024] Upon vibration of a vibration member, opposite ends of thedeflection optical waveguide region in the discontinuous region displacerelatively toward the vibration direction of the vibration member. Theleak light quantity of light leaking from the deflection opticalwaveguide region to the outside of the discontinuous region is largewhen the relative displacement of the opposite ends is small, andincreases when it is large. In this manner, the light propagationquantity between both ends of the optical waveguide can be changed withvibration of the vibration member.

[0025] According to a vibration detector of a thirteenth invention, inthe vibration detector of the seventh, eighth or twelfth invention, thediaphragm is a diaphragm having a vibration direction and a thicknessdirection which are coincident with each other; the deflection opticalwaveguide region of the optical waveguide has one discontinuous regionat a position corresponding to the deflection region of the diaphragm,and one deflection optical waveguide region is provided on the side ofthe light emitting element of the optical waveguide relative to thediscontinuous region and two deflection optical waveguide regions areprovided on the side of the light receiving element; the one deflectionoptical waveguide region is disposed in a central area of the diaphragmalong the thickness direction of the diaphragm, and the two deflectionoptical waveguide regions are disposed in front and back areas of thecentral area; end positions of each of the deflection optical waveguideregions confronting with each other with the discontinuous region beinginterposed therebetween relatively displace toward a vibration directionin response to vibration of the diaphragm; and in accordance with therelative displacement, a leak light quantity of light from thediscontinuous region of each of the deflection optical waveguide regionschanges.

[0026] Front and back surfaces of the central area of the diaphragmalong the thickness direction have the relation (expansion on onesurface and contraction on the other surface) that the reverse positiveand negative reflections relative to vibration of the diaphragm.Therefore, by using a difference between the output light quantities ofboth the light receiving elements, an output having a small variation tobe caused by manufacture variations of diaphragms can be obtained.

[0027] According to a vibration detector of a fourteenth invention, inthe vibration detector of any one of the seventh to thirteenthinvention, the diaphragm, the optical waveguide and the opticalwaveguide holder are integrally made of one plate of opticallytransmissive material.

[0028] In forming the optical waveguide from one plate of opticallytransmissive material, for example, thermal diffusion or ionimplantation adopted by semiconductor manufacture techniques may beused. Predetermined optically transmissive material (e.g., lithiumnitrate LiNO₃) is selectively subjected to an ion exchange process. Withthis ion exchange process, a refractive index of the portionion-exchanged is changed from that of the portion not ion-exchanged.

[0029] According to a vibration detector of a fifteenth invention, inthe vibration detector of the fourteenth invention, the diaphragm isformed with line-shaped through holes or grooves to improve deflectionof the deflection region of the diaphragm.

[0030] The line-shaped through holes or grooves in the diaphragm areformed extending along the radiation direction and/or circumferencedirection of the diaphragm. Since the optically transmissive materialhas a relatively high rigidity, proper deflection can be obtained byforming through holes or grooves.

[0031] The discontinuous region of the optical waveguide is preferablyformed at the position associated with the through hole or groove. Byforming the line-shaped through hole or groove at a specific position ofthe diaphragm, defection of the diaphragm at the specific position canbe increased. By disposing the discontinuous region of the opticalwaveguide at the position corresponding to the position having theincreased deflection, the characteristics of the light propagationquantity between both ends of the optical waveguide can be improvedrelative to vibration of the diaphragm.

[0032] According to a vibration detector of a sixteenth invention, inthe vibration detector of the seventh invention, the diaphragm is adiaphragm having a vibration direction and a thickness direction whichare coincident with each other; the proper number of the opticalwaveguide holders for holding the diaphragm to the optical waveguide aredisposed along a thickness direction of the diaphragm; light of the samequantity is made incident upon each of the optical waveguides from thelight emitting element mounted on one end of each of the proper numberof the optical waveguide holders; and the light receiving elementmounted on the other end of each of the proper number of the opticalwaveguide holders detects a quantity of light output from each of theoptical waveguides.

[0033] By processing a predetermined combination of light propagationquantities between both ends of each optical waveguide distributed alongthe width direction of the diaphragm, an electric signal preciselyreflecting a vibration amplitude of the diaphragm can be obtained.

[0034] According to a vibration detector of a seventeenth invention, inthe vibration detector of the fourteenth or fifteenth invention, thediaphragm and the optical waveguide holder are substantially circular;and the light emitting element and the light receiving element opticallycoupled to the optical waveguide holder are mounted on a flexiblesubstrate which surrounds a peripheral area of the diaphragm and theoptical waveguide holder.

[0035] For the interconnection between electrical wiring lines andelements on the flexible substrate, a flipchip structure is preferablyused. By using the flexible substrate, optical connection between thelight emitting element, light receiving element and optical waveguideand lamination assembly can be performed smoothly.

[0036] According to a vibration detector of an eighteenth invention, inthe vibration detector of the fourteenth or fifteenth invention, aperipheral area of the diaphragm and the optical waveguide holder aresandwiched between ceramic layers and the light emitting element and thelight receiving element optically coupled to the optical waveguideholder are embedded in a plurality of ceramic layers.

[0037] Since the diaphragm, light emitting element and light receivingelement can be formed as a module, a manufacture efficiency can beimproved.

BRIEF DESCRIPTION OF THE DRAWINGS

[0038]FIG. 1 is a vertical cross sectional view of a light detectiontype microphone.

[0039]FIG. 2 is a front view of a sound pressure detector module shownin FIG. 1.

[0040]FIG. 3 is a vertical cross sectional view of a diaphragm shown inFIG. 2 and its mount structure.

[0041]FIG. 4 is a development diagram of a ring frame shown in FIG. 2.

[0042]FIG. 5 is a diagram illustrating a sound pressure detectionprinciple of a sound pressure detector module.

[0043]FIG. 6 is a cross sectional view of a sound pressure detectormodule having a ceramic layer lamination structure.

[0044] FIGS. 7(a) and 7(b) are a front view and a vertical crosssectional view showing a sound pressure detector module having anoptical waveguide with another structure.

[0045]FIG. 8 is a diagram showing leak light from a discontinuous regioncaused by deflection of the diaphragm shown in FIG. 7.

[0046] FIGS. 9(a) and 9(b) are a front view and a vertical crosssectional view showing a sound pressure detector module having acorrugated diaphragm.

[0047] FIGS. 10(a) and 10(b) are enlarged views of corrugated diaphragmsaccording to modifications.

[0048]FIG. 11 is a front view of a sound pressure detector module havinga diaphragm with recesses.

[0049]FIG. 12 is an enlarged cross sectional view of the diaphragm shownin FIG. 11.

[0050]FIG. 13 is a graph showing the relation between a displacementquantity of a diaphragm along a vibration direction and a total lightreception quantity of both light receiving elements.

[0051]FIG. 14 is a graph showing the relation between a displacementquantity of a diaphragm of the sound pressure detector module shown inFIG. 8 and a difference between light reception quantities of both lightreceiving elements.

[0052]FIG. 15 is a schematic diagram showing a known light detectiontype microphone.

[0053]FIG. 16 is a schematic diagram showing another known lightdetection type microphone.

[0054]FIG. 17 is a detailed diagram of the light detection typemicrophone shown in FIG. 16.

EMBODIMENTS OF THE INVENTION

[0055] Embodiments of the invention will be described with reference tothe accompanying drawings.

[0056]FIG. 1 is a vertical cross sectional view of a light detectiontype microphone 10. A front perforated cover 12 and a back perforatedcover 13 cover a front opening and a back opening of a cylindrical case11 extending along the axial direction. The front and back perforatedcovers 12 and 13 prevent dust and foreign matter from entering theinside of the cylindrical case 11 and permit propagation of a sound waveinto the cylindrical case 11. A circular sound pressure detector module17 is fixed, as viewed from the front side, to approximately the centralarea of the cylindrical case 11 along its axial direction, and has adiaphragm 27 whose periphery is supported by a ring frame 18. In FIG. 1,F represents a sound pressure, and A represents vibration of the soundpressure detector module 17 caused by the sound pressure F. The physicalvalues of the light detection type microphone 10 are as follows:

[0057] A length of the cylindrical case 11 along the axial direction: 10mm or shorter;

[0058] An outer diameter of the cylindrical case 11: 10 mm or shorter;

[0059] A thickness of the diaphragm 27: 10 im or thinner; and

[0060] A total weight of the light detection type microphone: 2 g orlighter.

[0061]FIG. 2 is a front view of the sound pressure detector module 17.The ring frame 18 surrounds the circumference of the diaphragm 27. Thediaphragm 27 is made of optically transmissive material and has anoptical waveguide 28 which extends in the inside of a diaphragm mainbody 29 along the diameter of the diaphragm 27.

[0062]FIG. 3 is a vertical cross sectional view of the diaphragm 27shown in FIG. 2 and its mount structure. In forming the opticalwaveguide 28 of the diaphragm 27, by utilizing semiconductor manufacturetechniques, the diaphragm (e.g., lithium nitrate LiNO₃) 27 is subjectedto an ion exchange process by masking the portion corresponding to theoptical waveguide 28. With this ion exchange process, a refractive indexof the portion ion-exchanged is lowered than that of the portion notion-exchanged which becomes the optical waveguide 28. In order that theoptical waveguide 28 changes a light propagation quantity between itsopposite ends in accordance with a deflection in its diameter directionor a thickness direction, i.e., a vibration direction of the diaphragm27, in other words, in order that the optical waveguide changes aquantity of light leaked to the outside of the optical waveguide 28 inaccordance with a deflection in the vibration direction of the opticalwaveguide 28, it is necessary to make thin the optical waveguide 28,e.g., the diameter or thickness of the optical waveguide 28 is set abouta tenfold or less than the wavelength of propagation light. A lightemitting element 20 and a light emission monitor 21 are fixed to bothsurfaces of the diaphragm 27 at one end of the optical waveguide 28.Light receiving elements 24 are fixed to both surfaces of the diaphragm27 at the other end of the optical waveguide 28. Diffraction opticalelements 33 are formed in the diaphragm 27 at opposite ends of theoptical waveguide 28 by ion implantation similar to the opticalwaveguide 28. Incident light from the light emitting element 20 into thediaphragm 27 is guided to the optical waveguide 28 by the diffractionoptical elements 33 at one end of the optical waveguide 28, and apredetermined quantity of the incident light is guided to the lightemission monitor element 21. The diffraction optical elements 33 at theother end of the optical waveguide 28 make light from the opticalwaveguide 28 become incident upon both the light receiving elements 24.

[0063]FIG. 4 is a development diagram of the ring frame 18 shown in FIG.2. The ring frame 18 has a flexible substrate 19 and various electricelements mounted on the flexible substrate by a flip-chip structure. Theflexible substrate 19 has: a pair of ring side plates 35 having acircular opening 37 for sandwiching the diaphragm 27; a coupling stripe36 for electrically connecting both the ring side plates 35; and a hookband 38 coupled to one ring side plate 35 for adhering both the ringside plates 35, with the periphery of the diaphragm 27 being sandwichedbetween the ring side plates 35 and with the ring side plates beingelectrically connected. On the ring side plate 35 having the hook band38, the light emission monitor element 21 and light receiving element 24are mounted at opposite ends along the diameter direction. Signalprocessing ICs 40 and 41 are mounted near at opposite ends of the lightemission monitor element 21. On the other ring side plate 35 coupled bythe hook band 38, the light emitting element 20 and light receivingelement 24 are mounted at opposite ends along the diameter direction.Signal processing ICs 40 and 41 are mounted near at opposite ends of thelight receiving element 24. Near at the light emitting element 20, alight emission automatic adjustment IC 39 is mounted. The light emissionautomatic adjustment IC 39 controls a supply power to the light emittingelement 20 in accordance with an output of the light emission monitorelement 21 to control the light emission quantity of the light emittingelement 20 to be constant. The signal processing IC 40 outputs anelectric signal corresponding to a calculated value (addition value inthe case of the sound pressure detector module 17) of a light receptionquantity of both the light receiving elements 24. The light emittingelement 20 is a semiconductor light source such as a light emittingdiode (LED) and a surface radiation semiconductor laser.

[0064]FIG. 5 is a diagram illustrating the sound pressure detectionprinciple of the sound pressure detector module 17. In FIG. 5, Arepresents a vibration direction of the diaphragm 27 caused by a soundpressure, and L represents leak light from the optical waveguide 28caused by a deflection of the optical waveguide 28. Upon reception of asound pressure, the diaphragm 27 vibrates in the thickness direction atan amplitude related to the sound pressure. As the diaphragm 27vibrates, the optical waveguide 28 deflects in the diameter direction orthickness direction. A lateral deflection of the diaphragm 27 causesleak light L to propagate to the outside of the optical waveguide 28. Aquantity of light leak from the optical waveguide 28 is related to adeflection quantity of the optical waveguide 28 in the diameter orthickness direction, i.e., a lateral deflection quantity and hence to asound pressure acting upon the diaphragm 27. As a result, a total lightquantity incident upon the optical waveguide 28 is related to the soundpressure. The signal processing IC 40 outputs an electric signalcorresponding to the sound pressure. FIG. 13 is a graph showing therelation between a displacement quantity of the diaphragm 27 in thevibration direction and a light reception quantity of both the lightreceiving elements 24. The displacement quantity of the diaphragm 27 ispositive in the front direction of the light detection type microphone10.

[0065]FIG. 6 is a cross sectional view of a sound pressure detectormodule 17 b having a lamination structure of ceramic layers 43. Fiveceramic layers 43 are stacked by exposing the diaphragm 27 except itsperipheral area. A plurality of electrodes 44 are exposed on the bottomsurface of the lowest ceramic layer 43. The light emitting element 20and one light receiving element 24 are disposed in the same layer asthat of the optical waveguide 28. For example, a Fabry-Perotsemiconductor laser of a facet radiation type is adopted as the lightemitting element 20. The diffraction optical elements 33 are formed onone side of the optical waveguide 28, only on the upper side as shown inFIG. 6.

[0066] FIGS. 7(a) and 7(b) are a front view and a vertical crosssectional view of a sound pressure detector module 17 c having anoptical waveguide 28 c with a different structure. In FIGS. 7(a) and7(b) showing the sound pressure detector module 17 c, identical elementsto those of the sound pressure detector module 17 shown in FIGS. 5 and 6are represented by using the same symbols, and corresponding elementsare represented by the symbol added with “c”. Only the important pointswill be described. The optical waveguide 28 c has a discontinuous region45 approximately in the central area of the diaphragm 27 c. The opticalwaveguide 28 c is divided by the discontinuous region 45 into anupstream region 46 on the side of the light emitting element 20 anddownstream regions 47 on the side of the light receiving element 24.There is one upstream region 46 which extends in the central area of thediaphragm 27 in the thickness direction. There are two downstreamregions 47 which extend in parallel in the front and back areas of thecentral area of the diaphragm 27 in the thickness direction. Thediameter of the upstream region 46 is larger than that of eachdownstream region 47. When the diaphragm 27 c is at the balancedposition (position with 0 deflection), output light propagatingstraightforward from the upstream region 46 is divided approximatelyequally and enters each downstream region 47.

[0067]FIG. 8 shows leak light L from the discontinuous region 45 causedby a deflection of the diaphragm 27 c shown in FIG. 7. Referring toFIGS. 7 and 8, light from the light emitting element 20 becomes incidentupon the upstream region 46 and is guided in the upstream region 46toward the discontinuous region 45, and output from the end of theupstream region 46 on the side of the discontinuous region 45 to thediscontinuous region 45. Part of the output light to the discontinuousregion 45 becomes leak light L and is leaked to the outside of thediaphragm 27 c, whereas the remaining light becomes incident upon thetwo downstream regions 47 and is guided in the downstream regions 47toward the light receiving elements 24. Upon reception of a soundpressure, the diaphragm 27 c vibrates. When the diaphragm 27 c is at thebalanced position, i.e., when a defection quantity of the diaphragm 27 cis 0, light of the same quantity Q becomes incident upon each downstreamregion 47 from the upstream region 46. When the diaphragm 27 c has aconvex deflection in one direction, there is a relative shift betweenthe upstream region 46 and each downstream region 47 of the diaphragm 27c in the vibration direction. Therefore, light having a quantity Q+ÄQand light having a quantity Q−ÄQ become incident upon the downstreamregions 47 from the upstream region 46. A difference between the lightreception quantities of both the light receiving elements 24 istherefore 2·ÄQ relative to the sound pressure, including the casewherein the displacement quantity of the diaphragm 27 c is 0.

[0068]FIG. 14 is a graph showing the relation between a displacementquantity of the diaphragm 27 c of the sound pressure detector module 17c shown in FIG. 8 and a difference between the light receptionquantities of both the light receiving elements 24. The displacementquantity of the diaphragm 27 c is positive in the front direction of thelight detection type microphone 10.

[0069] FIGS. 9(a) and 9(b) are a front view and a vertical crosssectional view of a sound pressure detector module 17 d having acorrugated diaphragm 27 d. In FIGS. 9(a) and 9(b) showing the soundpressure detector module 17 d, identical elements to those of the soundpressure detector modules 17 and 17 c shown in FIGS. 5 and 8 arerepresented by using the same symbols, and corresponding elements arerepresented by the symbol added with “d”. Only the important points willbe described. The diaphragm 27 d is divided at a border line 51 into aninner central corrugated thick region 49 and a flat region 50 in anouter peripheral area. On each of the front and back surfaces of thediaphragm 27 d, a convex portion and a concave portion are alternatelydisposed in the radius direction, and the convex portion on one surfaceis formed at the position corresponding to that of the concave portionon the other surface in order to make uniform the thickness of thediaphragm 27 d along the radius direction. Lines on the convex portionsas viewed from the front side of the diaphragm 27 d are represented bytwo border lines 52. The optical waveguide 28 d has discontinuousregions 53 in the area from the outer one flat region 50 to the otherflat region 50 as viewed in plan. In FIG. 9, the optical waveguide 28 dhas five discontinuous regions 53. The corrugated thick region 49increases deflection of the diaphragm 27 d more than the flat structure.The corrugated thick region 49 has also a function of regulating adeflection direction. By aligning the deflection direction of thediaphragm 27 d with the sound pressure reception direction, a deflectionquantity per sound pressure can be increased.

[0070]FIG. 10 is enlarged views of corrugated diaphragms according tomodifications. In FIGS. 10(a) to 10(c) showing the corrugated diaphragms27 e, 27 f and 27 g, identical elements to those of the diaphragm 27 dshown in FIG. 9 are represented by using the same symbols, thedescription thereof is omitted, and corresponding elements arerepresented by changing “d” to “e”, “f” or “g”. On each of the front andback surfaces of the diaphragm 27 d, 27 f, a convex portion 64 and aconcave portion 65 are alternately disposed in the radius direction, andthe convex portion 64 on one surface is formed at the positioncorresponding to that of the concave portion 65 on the other surface atthe same radius direction position in order to make uniform thethickness of the diaphragm 27 e, 27 f along the radius direction. Theoptical waveguide 28 e of the diaphragm 27 e shown in FIG. 10(a) and theoptical waveguide 28 f of the diaphragm 27 f shown in FIG. 10(b) extendin the diaphragm main bodies 29 e and 29 f in a waving manner along thecorrugated shapes of the diaphragms 28 e and 28 f. The optical waveguide28 e of the diaphragm 27 e is continuous, whereas the optical waveguide28 f of the diaphragm 27 f has a plurality of discontinuous regions 53.In order to align the phase of the diaphragm 27 f during vibration, thediscontinuous region 53 is formed at the position corresponding to thatof the convex portion 64 on one surface at the same radius position. Thediaphragm 27 g shown in FIG. 10(c) is a modification of the diaphragm 27f. In this diaphragm 27 g, the convex portion 64 on one surface isformed at the position corresponding to that of the convex portion 64 onthe other surface, and the concave portion 65 on one surface is formedat the position corresponding to that of the concave portion 65 on theother surface, respectively at the same radius position. The rigidity ofthe diaphragm 27 g at the radius direction position where the concaveportion 65 is formed becomes lower than that at the radius directionposition where the convex portion 64 is formed, so that the diaphragm iseasy to be deflected. The discontinuous region 53 is formed in this areawhich is easy to be deflected. A quantity of leak light L caused by avibration of the diaphragm 27 g can change considerably.

[0071]FIG. 11 is a front view of a sound pressure detector module 17 hhaving a diaphragm 27 h with recesses 58, and FIG. 12 is an enlargedcross sectional view of the diaphragm 27 h. In FIGS. 11 and 12 showingthe sound pressure detector module 17 h, identical elements to those ofthe sound pressure detector module 17 are represented by using the samesymbols, and corresponding elements are represented by the symbol addedwith “h”. Only the important points will be described. The diaphragm 27h has a circle flat region 55, a central ring region 56 and a peripheralflat region 57 in this order from the central area in the radiusdirection. As shown in FIG. 12, the circle flat region 55 protrudesalong the axial direction of the diaphragm 27 h relative to theperipheral flat region 57. The central ring region 56 extends obliquelyrelative to the circle flat region 55 and peripheral flat region 57. Theoptical waveguide 28 h extends in the diaphragm main body 29 h along thesectional contour line of the diaphragm 27 h. A border line 59 shown inFIG. 11 indicates the border between the circle flat region 55 andcentral ring region 56, a border line 60 indicates the border betweenthe central ring region 56 and peripheral flat region 57. A plurality ofrecesses 58 are formed through the central ring region 56 at an equalangle pitch along the circumference direction. The width of each recess58 is exaggerated in FIG. 11 and is actually 50 im. Flection of thecentral ring region 56 can be increased by the recesses 58. The opticalwaveguide 28 h has discontinuous regions 61 near at cross points withthe border lines 59 and 60. There are four discontinuous regions 61 intotal. Upon reception of a sound pressure, the diaphragm 27 h has alargest deflection in the vibration direction at the positionscorresponding to the border lines 59 and 60. By setting thediscontinuous regions 61 to the positions where the largest deflectionof the diaphragm 27 h occurs, a change in the light propagation quantitybetween opposite ends of the optical waveguide 28 h increases relativeto a unit change quantity of a sound pressure.

What is claimed is:
 1. A vibration detector comprising: a diaphragmwhich vibrates upon reception of vibration; and an optical waveguidewhich extends along a direction of a flat plane of said diaphragm andequipped with said diaphragm to vibrate integrally with said diaphragm,wherein: in accordance with deformation of said optical waveguide causedby vibration of said diaphragm, a leak light quantity of light enteredfrom one end of said optical waveguide and leaked to an outside of saidoptical waveguide changes and a light propagation quantity of the lightpropagated to the other end of said optical waveguide changes; and adisplacement of said diaphragm caused by the vibration is detected bydetecting a change in the light propagation quantity of said opticalwaveguide.
 2. A vibration detector according to claim 1, wherein: inaccordance with the deformation of said optical waveguide caused byvibration of said diaphragm, a material density of a deformed portion ofsaid optical waveguide changes to thereby change a refractive index ofthe deformed portion; and the leak light quantity of light from saidoptical waveguide changes with a change in the refractive index.
 3. Avibration detector according to claim 1, wherein a diameter or thicknessof said optical waveguide along a vibration direction of said diaphragmis set so that the leak light quantity of light from said opticalwaveguide changes more or less in accordance with the deformation ofsaid optical waveguide.
 4. A vibration detector according to claim 1,wherein a refractive index of said optical waveguide is set irregularlyso that the leak light quantity of light from said optical waveguidechanges with the deformation of said optical waveguide.
 5. A vibrationdetector according to claim 1, wherein: said optical waveguide has adiscontinuous region at a proper position along an extension directionof said optical waveguide; end positions of said optical waveguideconfronting with each other with said discontinuous region beinginterposed therebetween relatively displace toward a vibration directionin response to the vibration of said diaphragm; and in accordance withthe relative displacement, the leak light quantity of light from saiddiscontinuous region of said optical waveguide changes.
 6. A vibrationdetector according to claim 1, wherein said optical waveguide isequipped in said diaphragm.
 7. A vibration detector comprising:. adiaphragm having a deflection region which deflects along a vibrationdirection upon reception of vibration; an optical waveguide having adeflection optical waveguide region which deflects integrally with adeflection region of said diaphragm wherein a light propagation quantitychanges with deflection of the deflection optical waveguide region; alight emitting element for making light become incident upon one end ofsaid optical waveguide; and a light receiving element for receivinglight output from the other end of said optical waveguide and outputtinga change in the light propagation quantity of said optical waveguide asan electric signal representative of a displacement quantity of thedeflection region of said diaphragm.
 8. A vibration detector accordingto claim 7, wherein said optical waveguide together with said diaphragmis held by an optical waveguide holder and optically coupled to saidlight emitting element and said light receiving element via said opticalwaveguide holder.
 9. A vibration detector according to claim 7, wherein:said deflection optical waveguide region of said optical waveguide isformed continuously in an area corresponding to the deflection region ofsaid diaphragm; in accordance with deformation of said deflectionoptical waveguide region caused by vibration of said diaphragm, amaterial density of said reflection optical waveguide region changes tothereby change a refractive index of said deflection optical waveguideregion; and a leak light quantity of light from said deflection opticalwaveguide region changes with a change in the refractive index.
 10. Avibration detector according to claim 7, wherein: said deflectionoptical waveguide region of said optical waveguide is formedcontinuously in an area corresponding to the deflection region of saiddiaphragm; and a diameter or thickness of said deflection opticalwaveguide region along a vibration direction of said diaphragm is set sothat a leak light quantity of light from said deflection opticalwaveguide changes more or less in accordance with deformation of saiddeflection optical waveguide region caused by vibration of saiddiaphragm.
 11. A vibration detector according to claim 7, wherein: saiddeflection optical waveguide region of said optical waveguide is formedcontinuously in an area corresponding to the deflection region of saiddiaphragm; and a refractive index of said deflection optical waveguideregion is set irregularly so that a leak light quantity of light fromsaid deflection optical waveguide region changes with deformation ofsaid deflection optical waveguide region.
 12. A vibration detectoraccording to claim 7, wherein: said deflection optical waveguide regionof said optical waveguide has a discontinuous region at a positioncorresponding to the deflection region of said diaphragm; end positionsof said deflection optical waveguide region confronting with each otherwith said discontinuous region being interposed therebetween relativelydisplace toward a vibration direction in response to the vibration ofsaid diaphragm; and in accordance with the relative displacement, a leaklight quantity of light from said discontinuous region changes.
 13. Avibration detector according to any one of claims 7, 8 and 12, wherein:said diaphragm is a diaphragm having a vibration direction and athickness direction which are coincident with each other; saiddeflection optical waveguide region of said optical waveguide has onediscontinuous region at a position corresponding to the deflectionregion of said diaphragm, and one deflection optical waveguide region isprovided on the side of said light emitting element of said opticalwaveguide relative to said discontinuous region and two deflectionoptical waveguide regions are provided on the side of said lightreceiving element; said one deflection optical waveguide region isdisposed in a central area of said diaphragm along the thicknessdirection of said diaphragm, and said two deflection optical waveguideregions are disposed in front and back areas of the central area; endpositions of each of said deflection optical waveguide regionsconfronting with each other with said discontinuous region beinginterposed therebetween relatively displace toward a vibration directionin response to vibration of said diaphragm; and in accordance with therelative displacement, a leak light quantity of light from saiddiscontinuous region of each of said deflection optical waveguideregions changes.
 14. A vibration detector according to any one of claims7 to 13, wherein said diaphragm, said optical waveguide and the opticalwaveguide holder are integrally made of one plate of opticallytransmissive material.
 15. A vibration detector according to any one ofclaims 7 to 14, wherein said diaphragm is formed with line-shapedthrough holes or grooves to improve deflection of the deflection regionof said diaphragm.
 16. A vibration detector according to any one ofclaims 7 to 15, wherein: said diaphragm is a diaphragm having avibration direction and a thickness direction which are coincident witheach other; the proper number of the optical waveguide holders forholding said diaphragm to said optical waveguide are disposed along athickness direction of said diaphragm; light of the same quantity ismade incident upon each of said optical waveguides from said lightemitting element mounted on one end of each of the proper number of theoptical waveguide holders; and said light receiving element mounted onthe other end of each of the proper number of the optical waveguideholders detects a quantity of light output from each of said opticalwaveguides.
 17. A vibration detector according to claim 14 or 15,wherein: said diaphragm and the optical waveguide holder aresubstantially circular; and said light emitting element and said lightreceiving element optically coupled to the optical waveguide holder aremounted on a flexible substrate which surrounds a peripheral area ofsaid diaphragm and the optical waveguide holder.
 18. A vibrationdetector according to claim 14 or 15, wherein a peripheral area of saiddiaphragm and the optical waveguide holder are sandwiched betweenceramic layers and said light emitting element and said light receivingelement optically coupled to the optical waveguide holder are embeddedin a plurality of ceramic layers.